<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Document</title>
    </head>
    <body>
        <div id="box" class="hello world" data-hello="123" data-world="345" style="color: red;font-size:50px;">
            hello, world
        </div>

        <script>
            var box = document.querySelector('#box');

            console.log(box);

            console.log(box.getAttribute('date-hello'));
            console.log(box.dataset.hello);

            box.dataset.hello = 100;
        </script>
    </body>
</html>